1. Field of the Invention
The present invention relates to a display device, a method for manufacturing the display device and an apparatus for manufacturing the display device. In particular, the invention relates to a display device formed over a flexible substrate that can be bent, a method for manufacturing thereof and an apparatus for manufacturing thereof.
2. Description of the Related Art
In recent years, research and development of display devices using light emitting elements have been carried out actively. The display devices using the light emitting elements do not require backlights unlike display devices using liquid crystal and the like. Further, the display devices using the light emitting elements also have advantages of high viewing angle and the like. Also, film-type display devices that can be bent themselves have been attracting attention, recently.
Methods for manufacturing the film-type display devices are mainly classified into two types. In one method for manufacturing the film-type display device, a flexible substrate such as plastic is prepared in advance, and circuit patterns such as a wiring and a pixel electrode are directly formed over the substrate by using a metal material or an insulating material. In another method for manufacturing the film-type display device, circuit patterns such as a wiring and a pixel electrode are formed over a substrate with rigidity such as glass in advance by using a metal material and an insulating materials, and then only the substrate with rigidity is grinded or polished to be reduced in thickness or the substrate with the rigidity is replaced by a flexible substrate.
However, when a film-type display device is manufactured by directly forming a metal material or an insulating material over a flexible substrate made from plastic or the like, manufacturing conditions are limited due to a heat resistance property of the substrate and the like. That is, the display device should be manufactured in consideration of various sorts of resistance properties such as the heat resistance property and the strength of the flexible substrate. For example, in the case of forming pixels, driver circuits and the like of a display device are formed using thin film transistors (TFTs), conditions of a heat treatment and the like are limited so that a semiconductor film cannot be crystallized sufficiently. Therefore, TFTs having excellent characteristics cannot be obtained.
On the other hand, when a film-type display device is formed by forming a display device over a substrate with rigidity such as a glass substrate, separating the display device from the substrate with the rigidity and transferring to a flexible substrate, there are a problem of disconnection of a wiring and the like due to stress applied to the display device in separation and a problem where a large size display device is difficult to be manufactured since the size of the display device depends on the size of the substrate (which is the glass substrate here).